[NOD-1502] Implement RestorePastUTXOSetIterator (#993)

* [NOD-1502] Implement RestorePastUTXOSetIterator

* [NOD-1502] Rename newUtxoSetIterator->newUTXOSetIterator

domain/consensus/datastructures/consensusstatestore/consensusstatestore.go

@@ -53,3 +53,7 @@ func (c consensusStateStore) Tips(dbContext model.DBReader) ([]*externalapi.Doma
 func (c consensusStateStore) StageTips(tipHashes []*externalapi.DomainHash) error {
 	panic("implement me")
 }
+
+func (c consensusStateStore) VirtualUTXOSetIterator(dbContext model.DBReader) (model.ReadOnlyUTXOSetIterator, error) {
+	panic("implement me")
+}

domain/consensus/model/interface_datastructures_consensusstatestore.go

@@ -10,6 +10,7 @@ type ConsensusStateStore interface {
 	StageVirtualUTXODiff(virtualUTXODiff *UTXODiff)
 	UTXOByOutpoint(dbContext DBReader, outpoint *externalapi.DomainOutpoint) (*externalapi.UTXOEntry, error)
 	HasUTXOByOutpoint(dbContext DBReader, outpoint *externalapi.DomainOutpoint) (bool, error)
+	VirtualUTXOSetIterator(dbContext DBReader) (ReadOnlyUTXOSetIterator, error)
 
 	StageVirtualDiffParents(virtualDiffParents []*externalapi.DomainHash) error
 	VirtualDiffParents(dbContext DBReader) ([]*externalapi.DomainHash, error)

domain/consensus/model/interface_processes_consensusstatemanager.go

@@ -7,4 +7,5 @@ type ConsensusStateManager interface {
 	AddBlockToVirtual(blockHash *externalapi.DomainHash) error
 	PopulateTransactionWithUTXOEntries(transaction *externalapi.DomainTransaction) error
 	SetPruningPointUTXOSet(pruningPoint *externalapi.DomainHash, serializedUTXOSet []byte) error
+	RestorePastUTXOSetIterator(blockHash *externalapi.DomainHash) (ReadOnlyUTXOSetIterator, error)
 }

domain/consensus/processes/consensusstatemanager/calculate_past_utxo.go

@@ -165,3 +165,65 @@ func (csm *consensusStateManager) checkTransactionMass(
 
 	return true, accumulatedMassAfter
 }
+
+func (csm *consensusStateManager) RestorePastUTXOSetIterator(blockHash *externalapi.DomainHash) (model.ReadOnlyUTXOSetIterator, error) {
+	diff, _, _, err := csm.calculatePastUTXOAndAcceptanceData(blockHash)
+	if err != nil {
+		return nil, err
+	}
+
+	virtualUTXOSetIterator, err := csm.consensusStateStore.VirtualUTXOSetIterator(csm.databaseContext)
+	if err != nil {
+		return nil, err
+	}
+
+	pastUTXO := model.NewUTXODiff()
+	for virtualUTXOSetIterator.Next() {
+		outpoint, utxoEntry := virtualUTXOSetIterator.Get()
+		pastUTXO.ToAdd[*outpoint] = utxoEntry
+	}
+
+	diff, err = utxoalgebra.WithDiff(pastUTXO, diff)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(diff.ToRemove) > 0 {
+		return nil, errors.New("diff.ToRemove is expected to be empty")
+	}
+
+	return newUTXOSetIterator(diff.ToAdd), nil
+}
+
+type utxoOutpointEntryPair struct {
+	outpoint externalapi.DomainOutpoint
+	entry    *externalapi.UTXOEntry
+}
+
+type utxoSetIterator struct {
+	index int
+	pairs []utxoOutpointEntryPair
+}
+
+func newUTXOSetIterator(collection model.UTXOCollection) *utxoSetIterator {
+	pairs := make([]utxoOutpointEntryPair, len(collection))
+	i := 0
+	for outpoint, entry := range collection {
+		pairs[i] = utxoOutpointEntryPair{
+			outpoint: outpoint,
+			entry:    entry,
+		}
+		i++
+	}
+	return &utxoSetIterator{index: 0, pairs: pairs}
+}
+
+func (u utxoSetIterator) Next() bool {
+	u.index++
+	return u.index != len(u.pairs)
+}
+
+func (u utxoSetIterator) Get() (outpoint *externalapi.DomainOutpoint, utxoEntry *externalapi.UTXOEntry) {
+	pair := u.pairs[u.index]
+	return &pair.outpoint, pair.entry
+}

domain/consensus/processes/consensusstatemanager/pick_virtual_parents.go

@@ -137,8 +137,12 @@ func (csm *consensusStateManager) mergeSetIncrease(
 
 func (csm *consensusStateManager) boundedMergeBreakingParents(parents []*externalapi.DomainHash) (hashset.HashSet, error) {
 	// Temporarily set virtual to all parents, so that we can run ghostdag on it
-	csm.dagTopologyManager.SetParents(model.VirtualBlockHash, parents)
-	err := csm.ghostdagManager.GHOSTDAG(model.VirtualBlockHash)
+	err := csm.dagTopologyManager.SetParents(model.VirtualBlockHash, parents)
+	if err != nil {
+		return nil, err
+	}
+
+	err = csm.ghostdagManager.GHOSTDAG(model.VirtualBlockHash)
 	if err != nil {
 		return nil, err
 	}

domain/consensus/processes/consensusstatemanager/update_virtual.go

@@ -13,7 +13,10 @@ func (csm *consensusStateManager) updateVirtual(newBlockHash *externalapi.Domain
 		return err
 	}
 
-	csm.dagTopologyManager.SetParents(model.VirtualBlockHash, virtualParents)
+	err = csm.dagTopologyManager.SetParents(model.VirtualBlockHash, virtualParents)
+	if err != nil {
+		return err
+	}
 
 	err = csm.ghostdagManager.GHOSTDAG(model.VirtualBlockHash)
 	if err != nil {